Toronto, 15 August 2011 | AFP

Sam Stosur has been defeated by Serena Williams in the final of the WTA Rogers Cup, going down 6-4 6-2 in Toronto on Sunday.

Williams hammered home her credentials as a US Open favourite when the last grand slam event of the season starts in two weeks’ time.

She fired nine aces and won 89 percent of her first serve points in beating Stosur in straight sets at the USD$2.05 million (AUD$1.98 million) hard court tournament, two weeks after winning the Stanford title.

The 29-year-old Williams is currently ranked 80th in the world and was competing in just her fourth tournament since being sidelined for a year by injuries and illness.

Her win over Stosur took just 77 minutes as the American served notice that she is returing to form just ahead of the 2011 US Open.